Poppy cultivation in Afghanistan is expected to soar by 59% this year, providing 92% of the world's supply of opium, the United Nations says.

The UN Office on Drugs and Crime predicted a 6,100-tonne harvest of opium, with much of the rise coming in Taleban strongholds in the south.

The US is the main backer of a huge drive to rid Afghanistan of opium.

But a top US drugs official warned on Saturday Afghanistan could be "taken down by this whole drug problem".

The $2.7bn drugs trade accounts for about a third of Afghanistan's economy.

Signs of collapse

The Vienna-based Office on Drugs and Crime said in its report that poppy cultivation in Helmand province alone, which has seen a sharp rise in Taleban-led attacks on international troops, had risen by 162% since last year.

This country is so fledgling, so fragile, and you've got a narco-economy now

Doug Wankel, director, US drugs control office

Only six of the country's 34 provinces are opium-free, the report says.

Office chief Antonio Maria Costa said after presenting his report to Afghan President Hamid Karzai: "These are very alarming numbers. Afghanistan is increasingly hooked on its own drug."

Mr Costa said southern Afghanistan was showing signs of collapse.

Rises also occurred in the north-east, where warlords and weak government were often to blame, the report said.

"Public opinion is increasingly frustrated by the fact that opium cultivation in Afghanistan is out of control," Mr Costa said.

"The political, military and economic investments by coalition countries are not having much visible impact on drug cultivation."

The UN urged Hamid Karzai to make "arrests and convictions"

He called on President Karzai to make "significant arrests and convictions" using the judiciary that the coalition had helped train and establish.

A massive programme to destroy poppies and offer help to farmers to grow alternative crops has been under way for two years.

But on Saturday, Doug Wankel, director of the US drugs control office, said Afghanistan could be "taken down" by drugs.

"If this thing gets out of hand, you could move from a narco-economy to a narco-state," he said.

"Then you have a very difficult chance for this country being able to achieve what it needs to as a democracy and a nation representing its people."